I don't really understand how a medication would help, unless it is to decrease the amount of saliva produced. But, CP doesn't cause production of excess saliva, it causes problems with muscles. Meaning--she is probably drooling (that's the same thing as slobbering, right?
) because her oral/lip muscles are weak and she can't keep it in!
Have her doctors mentioned any speech therapy? SLPs can do oral-motor therapy to try to strengthen the muscles...can she do things suck as pucker, move her lips and tongue from side-to-side, etc?
I would try speech therapy...in the meantime, you could do "games" such as making fish faces, having her try to hold a fruit loop (or something else round) in her lips to make an "O", tongue stuff such as holding a lollipop out in front of her and having her extend her tongue to lick it......
Hope you find something that works!